Spool valve with cavitation-minimizing valve assembly



July 26, 1966 H. J. STACEY 3,262,467

SPOOL VALVE WITH CAVITATIONMINIMIZING VALVE ASSEMBLY Filed July 27, 1964 IN VENTOR Hue/4 J. STA (5v United States Patent 3,262,467 SlPtDOL VALVE WITH CAVITATION-MINIMIZING VALVE ASSEMBLY Hugh 1. Stacey, Chesterland, Ohio, assignor to Parker- Hanuifin Corporation, Cleveland, Ohio, a corporation of Ohio Filed July 27, 1964, Ser. No. 385,117 Claims. (Cl. 137596.2)

The present invention relates generally as indicated to a valve assembly and more particularly to a spool type valve assembly for controlling the actuation of a fluid motor.

In some hydraulic systems as are employed in connection with front end loaders, for example, the bucket tilt cylinder, when actuated to tilt the bucket forwardly to load-dumping position, has imposed thereon a negative load which creates the condition that the cylinder demands more fluid than can be supplied by the system pump and if that occurs, vacuum pockets may be created in the system or air may be introduced into the system. It is, of course, desired to tilt the bucket forwardly at a relatively rapid rate against a stop on the bottom so as to jar the bucket and thus free the contents thereof for complete dumping therefrom, but it is not feasible to enlarge the system pump so as to have that great a capacity. On the other hand, it is not feasible to restrict the return line from the bucket tilt cylinder to decrease the cylinder demand to less than the pump capacity because in that case the forward tilting of the bucket would be slower than desired. As a third alternative, restriction of the pressure line to the bucket tilt cylinder would not solve the problem because the negative load on the cylind'er would yet cause cavitation in the system, and consequent erratic operaiton when the bucket cylinder is actuated in a direction to tilt the bucket rearwardly for scooping a load thereinto.

Accordingly, it is a principal object of this invention to provide a spool type valve assembly for controlling the actuation of a fluid motor in which the valve spool itself is provided with a shuttle valve therewithin which opens fluid communication between the motor return line and the pressure inlet port of the valve assembly whenever the inlet pressure decreases to a value less than that in the return line, whereby cavitation is prevented while yet the fluid motor may have demand for fluid substantially greater than the pump capacity.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principle of the invention may be employed.

In said annexed drawing: 7

FIG. 1 is a front elevation view of a spool-type valve assembly embodying the present invention as used in the hydraulic system of a front end loader;

FIG. 2 is a side elevation view of the spool valve assembly as viewed from the right-hand side of FIG. 1; and

FIG. 3 is a cross-section view of an enlarged scale taken substantially along the line 3-3, FIG. 2.

Referring now more particularly to the drawing, and first to FIGS. 1 and 2, the valve assembly 1 herein shown is a two-spool valve assembly comprising a housing 2 provided with parallel bores 3 and 4 (see FIG. 3) in which the respective spools 5 and 6 are axially moved in opposite directions to control double-acting fluid motors hoist cylinder 7 may float.

7 and 8 connected to the respective motor ports 9; 9 and 10; 10. In the present case, the fluid motor 7 controlled by the spool 5 is the hoist cylinder for the boom 11 mounted on pivot 12 of tractor T, and the fluid motor 8 controlled by the spool 6 is the tilt control cylinder for the bucket 14 mounted on pivot 15 of boom 11. It can be seen that as the bucket 14 is tilted forwardly to dumping position through linkage 16-17 and by retraction of bucket tilt cylinder 8, the bucket 14 and the load therein, will tend to retract the cylinder 8 as does the fluid under pressure entering the rod end thereof. At this time, the cylinder 8 demands more fluid than can be supplied by the system pump 18.

Referring now, in addition, to FIG. 3, it can be seen that the housing 2 is provided with a pressure inlet port 19, and when both spools 5 and 6 are in neutral position ice as shown, said inlet port 19 is communicated with the.

return port 20 through a central bypass passage 21. Thus, pump 18 circulates fluid from the tank 23 through conduits 24, and 25, through the bypass passage 21 in housing 2, and through conduit 26 back into the tank 23.

The spool valve 5 herein is a four-way float spool, and as evident, when the spool 5 is moved to the right from its neutral position as shown in FIG.- 3 to boom hoist position, the bypass passage 21 is blocked thereby, and fluid under pressure in the inlet chamber 27 is conducted to the head end of the hoist cylinder 7 via the left check valve 28, left pressure feed passage 23, and left motor passage 31) which leads to left motor port 9. In this position of the spool 5, the right motor and return passages 30 and 31 are in fluid communication with each other whereby the fluid displaced from the rod end of the hoist cylinder 7 into the right motor port 9 is returned to the tank 23 via the return port 20 and return conduit 26.

When the spool 5 is shifted a like amount to the left of neutral to boom lower position, the operation of the hoist cylinder 7 is reversed, that is, fluid under pressure is conducted from the inlet chamber 27 to the rod end of the motor 7 via the right check valve 28, right feed passage 29, and right motor passage 30 which leads to right motor port 9, and fluid is returned to the tank 23 via the left motor and return passages 30 and 31. When the spool is shifted further leftward to the float position, the slots 32 and spool bore 34 place the motor passages 30 in communication with each other so that the piston in the In the present case, the weight of the boom 11 and bucket 14 tends to retract the cylinder 7, and to maintain a positive pressure in the rod end, there is provided an orifice 35 communicating with the spool bore 34 and with the right return passage 31 to return excess fluid. However, the orifice 35 builds up a positive pressure in this part of the system so as to preclude cavitation during such float operation. The left end of the spool 5 will be provided with a suitable yieldable detent and spring return mechanism 36 so that the operator of the equipment may shift the spool 5, for example, so that it will be retained in either its hoist position or its float position. A yieldable stop may be provided at the boom lower position of the spool 5 so that the operator may feel when the spool 5 is at that position but the spool 5 may be automatically returned to neutral position from boom lower position upon release of force on said spool 5.

As shown in FIG. 3, the spool 6 is reciprocable in the bore 4 of the housing 2, and intersecting said bore 4 starting at the middle, is the aforesaid bypass passage 21 motor ports 10, and straddling the motor passages 40 are return passages 31 which lead to the return port 20. Between the inlet chamber 27 and one return passage 31 is a pressure relief valve 41 which, as well known in the art, is arranged to open communication between the inlet chamber 27 and the return passage 31 whenever the pressure in the inlet chamber 27 exceeds the pressure for which the relief valve 41 has been preset. The spool 6 has associated with one end thereof a spring centering mechanism 42 which yieldably holds the spool 6 in the neutral position as shown. In said neutral position of said spool 6, the system pump 18 may freely circulate fluid through the bypass passage 21 and the piston in the bucket tilt cylinder 8 is locked against movement because the motor ports and passages are at that time blocked from communication with either the adjacent pressure feed and return passages 39 and 31.

The spool 6 is hollow and has axially slidable therein a shuttle valve 45 which is biased by the spring 46 against the stop 47 so that the land 48 thereof covers the passages 49 which lead to the spool groove 50. Extending through the land 51 on one side of the shuttle land 48 are passages 52, and leading through the land 53 from the chamber 54 on the other side of the shuttle land 48 is an orifice 56. The land 57 of the spool 6 has diametrically opposite flats 58 which provide desired degree of restriction to return flow for a purpose which will be presently described.

It can be seen that when the spool 6 is shifted to the right from the neutral position shown in FIG. 3, the bypass 21 will be closed, and the groove 59 will place the left feed and motor passages 39 and 40 in fluid communication with each other whereby fluid under pressure in the inlet chamber 27 will flow through the left check valve 60 into the left feed passage 39 and thence to the left motor passage 40 to the head end of the bucket tilt cylinder 8, thus to tip the bucket 14 rearward to loadholding position. In this position of the spool 6, the groove 61 communicates the right motor passage 40 with the right return passage '31, whereby the oil displaced from the rod end of the cylinder 8 will be returned to the tank 23 via the return port 20 and return conduit 26.

When the spool 6 is shifted in the opposite direction from its neutral position, that is, toward the left, the bypass pass-age 21 will again be closed, and fluid under pressure in the inlet chamber 27 may enter the shuttle valve spring chamber 54 through the orifice 56 to maintain the shuttle valve 45 in position blocking the passages 49. In such position of the spool 6, the groove 61 places the right feed and motor passages 39 and 40 in fluid communication with each other, whereby fluid under pressure from the inlet chamber 27 flows through the right check valve 60 to the right feed passage 3?, the right motor passage 40, and thence to the rod end of the cylinder 8 thus to roll the bucket 14 forwardly to loaddumping position. As evident, the weight or" the bucket 14 itself and of the load therein, acts in a direction to retract the cylinder 8 and except for the present invention, such movement would tend to be faster than the pump capacity, in which case there would be cavitation of the system. When the spool 6 is in the aforesaid position, the flats 58 restrict return fiow from the head end of the cylinder 8 through left motor passage 40 to the left return passage 31, whereby such negative load on the cylinder 8 builds up a pressure in the return circuit and inside the spool 6 via the passages 52, whereby when such return pressure exceeds the pressure in the inlet chamber 27 and in the chamber 54 by the amount of bias of the spring 46, the shuttle valve 45 will be moved to the right to uncover the passages 49, thereby to place the left motor passage 40 in fluid communication with the inlet chamber 27. In this way, additional fluid is conducted to the inlet chamber 27 to preclude cavitation as aforesaid even though the demand of the cylinder 8 greatly exceeds the capacity of pump 18.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A valve assembly for controlling actuation of a double acting fluid motor comprising a housing having a bore intersected at axially spaced intervals therealong by an inlet port for connection with a fluid pressure source, a return port for connection with a fluid reservoir, and a pair of motor ports for connection with such motor; a valve spool axially movable in said bore from a neutral position blocking fluid communication between said inlet port and both motor ports to an operating position communicating said inlet port with one motor port and said return port with the other motor port for actuating such motor in one direction; a shuttle valve inside said spool movable to communicate said other motor port with said inlet port in response to fluid pressure in said other motor port exceeding that in said inlet port as occasioned by a load on such motor tending to actuate it in such one direction; said spool having a groove which defines a flow restrictor with said bore between said other motor port and said return port when in said operating position thus to build up back pressure in said other motor port for shuttle valve actuation as aforesaid.

2. The valve assembly of claim 1 wherein said spool is axially movable to another operating position communicating said inlet port with said other motor port and said return port with said one motor port for actuating such motor in the opposite direction; wherein said spool has axially spaced apart passages leading radially therethrough and respectively communicating with said other motor port and said inlet port when said spool is in its first-mentioned operating position; and wherein said shuttle valve has a plunger portion which covers the passage leading to said inlet port and of which one side is exposed to fluid pressure in said other motor port through the passage leading thereto for movement thereby to uncover the passage leading to said inlet port; said passage to which one side of said plunger portion is exposed being covered by the wall of said bore when said spool is in said another position.

3. The valve assembly of claim 1 wherein said bore is also intersected axially therealong :by a bypass passage communicating at one end with said inlet port and at the other end with said return port, by a pair of pressure feed passages straddling said bypass passage and communicating with said return port, by a pair of motor passages straddling said pressure feed passages and communicating with said motor ports for connection with such motor, and by a pair of return passages straddling said motor passages and communicating with said return port; said valve spool when in said neutral position communicating said inlet port with said return port via said bypass passage and blocking communication between the adjacent feed and motor passages and between the ad jacent motor and return passages, and when in said operating position communicating one pressure feed passage with the adjacent motor passage and communicating the other motor passage with the adjacent return passage for actuating such motor in said one direction.

4. A valve assembly for controlling actuation of a double acting fluid motor comprising a housing having a bore intersected at axially spaced intervals therealong by an inlet port for connection with a fluid pressure source, a return port for connection with a fluid reservoir, and a pair of motor ports for connection with such motor; a valve spool axially movable in said bore from a neutral position blocking fluid communication between said inlet port and both motor ports to an operating position communicating said inlet port with one motor port and said return port With the other motor port for actuating such motor in one direction, said valve spool having a longitudinal bore therein with a stop adjacent one end and axially spaced apart radial passages res-pectively communicating said other motor port and said inlet port with said spool bore when said spool is in said operating position; a shuttle valve disposed in said spool bore, said shuttle valve having a plunger portion slidably engaging the Wall of said spool bore and an extension projecting from said plunger portion in the direction of said stop; and a spring in said spool bore biasing said shuttle valve to a position whereat said extension engages said stop and said plunger portion covers the passage leading to said inlet port and one side of said plunger portion is exposed to fluid pressure in said other motor port through the passage leading thereto, whereby a higher fluid pressure in said other motor port than in said inlet port will cause such shuttle valve to move to a position uncovering the passage leading to said inlet port so as to communicate said other motor port with said inlet port.

5. The valve assembly of claim 4 wherein said spool 'has a groove which defines a flow restrictor with said housing bore between said other motor port and said return port when said. spool is in said operating position thus to build up back pressure in said other motor port for shuttle valve actuation as aforesaid; and said spool is axially movable to another operating position communicating said inlet port with said other motor port through said groove and said return port with said one motor port for actuating such motor in the opposite direction; said passage to which one side of said plunger portion is exposed being covered by the Wall of said housing bore when said spool is in said another operat ing position.

References fi ted by the Examiner UNITED STATES PATENTS 2,783,745 3/1957 Stephens 137--625.69 3,006,372 10/1961 Ruhl 137--6l2.1

MARTEN P. SCHWADRON, Primary Examiner. 

1. A VALVE ASSEMBLY FOR CONTROLLING ACTUATION OF A DOUBLE ACTING FLUID MOTOR COMPRISING A HOUSING HAVING A BORE INTERSECTED AT AXIALLY SPACED INTERVALS THEREALONG BY AN INLET PORT FOR CONNECTION WITH A FLUID PRESSURE SOURCE, A RETURN PORT FOR CONNECTION WITH A FLUID RESERVOIR, AND A PAIR OF MOTOR PORTS FOR CONNECTION WITH SUCH MOTOR; A VALVE SPOOL AXIALLY MOVABLE IN SAID BORE FROM A NEUTRAL POSITION BLOCKING FLUID COMMUNICATION BETWEEN SAID INLET PORT AND BOTH MOTOR PORTS TO AN OPERATING POSITION COMMUNICATING SAID INLET PORT WITH ONE MOTOR PORT AND SAID RETURN PORT WITH THE OTHER MOTOR PORT FOR ACTUATING SUCH MOTOR IN ONE DIRECTION; A SHUTTLE VALVE INSIDE SAID SPOOL MOVABLE TO COMMUNICATE SAID OTHER MOTOR PORT WITH SAID INLET PORT IN RESPONSE TO FLUID PRESSURE IN SAID 